The atmosphere is a stew of gases and particles. Some affect climate. Others degrade air quality and threaten human health. Some do both. Some do neither. Many of them interact with and affect one other.

Other pollutants — notably sulfates and nitrates—create health problems but simultaneously reflect incoming sunlight and cool the climate. Some, like nitrogen oxide, are precursors to ozone, but also affect the abundance of the light- scattering pollutants that cool the climate.

All of this adds up to a question that keeps some climatologists up at night: Is it possible to reduce emissions of toxic air pollutants in a way that will mitigate global warming, or at least not make it worse?

For example, reducing black carbon has the potential to improve health and reduce global temperatures by as much as a degree. On the other hand, reducing sulfates—which industries often emit along with black carbon—could negate any reduction in warming that pollution controls might produce. (These are just a few examples from the dozens of gases and particles that scientists have to factor in tabulating Earth’s energy budget.)

Almut Arneth, a researcher from Lund University in Sweden, and colleagues, including NASA climatologist Nadine Unger, considered the question recently in a “perspectives” piece in Science. You can read the full paper here (though you may need to brush up on your atmospheric chemistry to understand the details). Unger and her coauthors sum the complicated situation up this way:

“Given the toxicity of pollutants, the question is not whether ever stricter air pollution controls will be implemented, but when and where. The jury is out on whether air pollution control will accelerate or mitigate climate change. Still, the studies available to date mostly suggest that air pollution control will accelerate warming in the coming decades.”

Giles was in Kanpur to man one of NASA’s AERONET stations in the region as part of the ongoing TIGERZ campaign. He spent 17 days in Kanpur hauling the instrument around and getting harassed by local police officers, the occasional herd of roaming sheep and dust storms. In between all that, he spent the bulk of his time collecting measurements to determine whether dust and soot can glom onto one another to create new types of hybrid aerosols.

They do, he found, a seemingly mundane point but one that’s of considerable interest to the scientists trying to sort out how these two types of aerosols affect the climate. He presented his results in detail this week to colleagues at the American Geophysical Union fall meeting in San Francisco.

I nabbed him after his talk in the afternoon, to have a beer and talk through his travels. I asked him what was the most memorable part of the trip to India. “Well, it was unbelievably hot,” he said with a laugh. “Temperatures routinely hit 105 degrees.”

And how was the air? “You’d get used to it after a while,” said Giles, “but, at first, in the taxi, we were holding our sleeves over our mouths just to avoid breathing the stuff.”

Giles and colleagues using sun photometers to measure aerosols from a rooftop in Kanpur. (Credit: Giles)

Field assistants tromped through bogs in Harriman, NY to collect sediment cores that NASA

scientist Dorothy Peteet is using to date the retreat of the Laurentide Ice Sheet. Credit: Peteet

I spent big chunks of my childhood mucking through the lakes and bogs of New England with my brothers and looking for any number of critters hidden in the silt.

Turtles, of course, were the main draw (minus the snappers, which we knew were capable of mangling a toe or finger with a passing chomp), but actually snagging one always was a rare treat. Bullfrogs, salamanders, and newts were our standard catch.

If only we’d had a microscope. Watching Goddard Institute for Space Studies (GISS) botanist Dorothy Peteet show images of tiny fragments of pollen, seeds, and fossils that settled to lake bottoms and sat largely unchanged for thousands of years reminded me of the extraordinary oddness–and beauty–that’s lurking in the most unsuspecting of places.

Look, for example, at this fossilized head shield of a daphnia, or water flea, which Peteet showed during presentations at GISS and the American Geophysical Union meeting last December. It’s a miniscule planktonic crustacean with a transparent body and a heart that beats visibly:

Or this statoblast, a peculiar little reproductive pod that can withstand desiccation and freezing and buds from aquatic creatures called bryozoans:

Or this one, a fossilized leaf of a fruit-bearing, cold-loving tundra plant, perhaps a blueberry:

Peteet isn’t poking around in the mud just for fun like my brothers and I did as kids, though. She’s collecting bog cores and scrutinizing the bits of fossilized plants and animals, which can be dated quite precisely using radiocarbon techniques, that turn up in the cores. Her goal is to pinpoint the timing of the collapse of the Laurentide Ice Sheet, a massive block of ice that stretched as far as Long Island during the peak of the last ice age. With Arctic ice currently undergoing rapid retreat, sorting out how the Laurentide Ice Sheet collapsed has big implications for understanding how climate change might proceed.

By analyzing material from some of the first creatures to colonize glacial lakes after the ice retreated, such as those water fleas, Peetet can estimate the date the ice sheet collapsed. Her findings suggests that the collapse occurred about 15,000 years ago, which would put it five-to-ten thousand years later than other dating techniques (particularly one influential technique that involves dating the beryllium from boulders dropped by the retreating ice sheet).

The Earth is a bit like the human body; its temperature is very finely balanced, and when it gets slightly out of whack, big things can happen. In the case of our home planet, gases in the atmosphere play a vital role in maintaining this delicate equilibrium, by balancing the absorption and emission of all the electromagnetic radiation (microwaves, infrared waves, ultraviolet light and visible light, for example) reaching the surface of the Earth.

As reported recently, the Earth is getting warmer. Scientists believe the main driver behind this warming trend is rising levels of man-made greenhouse gases. These gases, which we pump out into the air, act to trap heat radiation near the surface of the Earth that would otherwise be sent back out into space. Carbon dioxide (CO2) is the Paris Hilton of greenhouse gases, and gets a lot of face time because its concentration in the atmosphere has increased relatively rapidly since the Industrial Revolution. But methane, nitrous oxide, hydrofluorocarbons (HFCs), chlorofluorocarbons (CFCs) and perfluorocarbons (PFCs) are also important agents of global warming. Some of them are actually much more potent than CO2 and they stick around for hundreds to thousands of years longer. This has some scientists concerned that these B-listers could actually impact global temperatures significantly more than CO2.

In a new paper, Partha Bera and colleagues at NASA’s Ames Research Center and Purdue University put these gases under the microscope to find out exactly why they are such powerful heat trappers. They focus on CFCs, HFCs and PFCs — all chemicals containing fluorine or chlorine — that are used in medicine, fridges, and as solvents, among other things. By probing the molecular structure of these compounds, they have found that molecules containing several fluorine atoms are especially strong greenhouse gases, for two reasons. First, unlike many other atmospheric molecules, they can absorb radiation that makes it through our atmosphere from space. Second, they absorb the radiation (and trap the heat) very efficiently, because of the nature of the fluorine bonds inside them. (In technical terms, fluorine atoms create a larger separation of electric charge within the molecule, and this helps the molecular bonds absorb electromagnetic radiation more effectively.) HFCs and other fluorine-based gases have been called “the worst greenhouse gases you’ve never heard of.” Now we know why.

Until now, scientists had not looked in detail at the underlying physical or chemical causes that make some molecules better global warmers than others. Bera and colleagues say that their work should help improve our “understanding [of] the physical characteristics of greenhouse gases, and specifically what makes an efficient greenhouse gas on a molecular level.” They hope their findings will be used by industry to develop more environmentally-friendly materials.

Strange as it may seem, the most recent Image of the Week entry from the Climate and Radiation Branch at Goddard Space Flight Center suggests that air pollution does indeed exacerbate lightning storms. The graphic, created by Goddard meteorologist Thomas Bell, shows that rainfall and lightning rarely peaks over the weekend in the southeastern United States. In fact, lightning hasn’t peaked on a weekend during any year since 1998, Bell has shown after combing through meteorological data from 1998 to 2009. After publishing a number of scientific papers on the topic, Bell thinks he knows why: air pollution (which is at its highest levels midweek and lowest levels on the weekend) can strengthen thunderstorms, particularly in the unstable and humid air of the Southeast.

The figure shows the day of the week favored by rainfall and by lightning in each summer from 1998 to 2009 in the southeastern United States (click here for a map of the area included in the analysis). The “clock plots” on the left and right indicate the day of the week when mean activity was at a maximum. The numbers indicate the year the data comes from. The rain estimates are based on TRMM and other satellite observations. The lightning data were collected by ground stations that are part of the National Lightning Detection Network. Credit: NASA/Bell

To find out more, I ran some questions about the connection between pollution and lightning by Bell via email:

What On Earth: Why does air pollution have any bearing on lightning or rainfall, and why is the connection more noticeable over the Southeast than other parts of the country?

Thomas Bell: Our explanation is that the storms need to start their growth in a hot, humid environment to give the pollution “something to work with.” The pollution causes the storm to climb to higher altitudes, because it causes the cloud droplets being formed in the storm to be smaller than they would be in a clean environment. They’re lighter and are carried up higher than usual, where they freeze (releasing latent heat), which pumps the storm up more than would happen in clean air.

The environment needs to be hot in order to have the capacity to push the storm up to altitudes where freezing can occur. The environment also needs to be humid because when the storm grows more vigorously it “sucks” air at its base up more strongly, pulling in more moisture, which then provides additional energy to the storm as the moisture condenses during its climb. The western half of the country is fairly dry—even though it can be hot, there isn’t much “fuel” (moisture) to feed a storm when it tries to grow more vigorously. The Southeast is especially hot and humid in the summer, so that’s where the effect shows up best, according to our theory.

What On Earth: Are there particular types of air pollution that have more or less impact on rain and lightning?

Thomas Bell:

We don’t have a good answer to this as yet. The pollution should be the kind that affects cloud droplet growth. If we had to finger something, we’d probably choose the kinds of particulates that are emitted by diesel engines, because it seems that the weekly cycle in pollution is due, to a considerable extent, to the weekly cycle in transportation (probably trucking). More trucks are on the roads from Tue-Thu than they are the rest of the week. But this is more conjecture than a well-documented explanation.

NASA-funded researcher Ben Smith digs a snow pit at a West Antarctic Ice Sheet Divide core site to try to infer the annual rate of snowfall. Credit: Ben Smith

Researchers who study glaciers and polar dynamics often get into it for the love of the field work— the challenging terrain, technicological adventures, and thigh-deep snow.

Benjamin Smith, a researcher at the Polar Science Center at the University of Washington’s Applied Physics Laboratory, was no exception. As a fledgling physicist in the 1990s, his first summer job after college turned into an eye-opening adventure — a 3-month stint at the Kamb Ice Stream in Antarctica as a field assistant mapping buried crevasses with snow-penetrating radar. The rest, as they say, was history.

These days, Smith is enjoying a rare honor as one of two NASA-supported researchers to receive the Presidential Early Career Award for Scientists and Engineers (PECASE), awarded at a White House ceremony last month.

WhatOnEarth: Field work was your entry into studying glaciers. Are you involvedin Arctic or Antarctic field work now?

Smith: After a few years of field work, I discovered that though being out in cold is great, the quicker way to learn about glacier change is by doing remote sensing work. That requires a great deal of data analysis indoors. So with that notion, I got onboard as part of NASA’s ICESat I mission while working on my doctorate in physics.

WhatOnEarth: What work do you believe was the basis for your presidential award?

Smith: Well, I have a few projects that I’ve been fortunate enough to be involved in.

Not too long ago, I wrote a paper where we found that several lakes beneath the glaciers in Antarctica have gained or lost water in the last five years, and at a rate much faster than things usually happen in Antarctica. We’ve been seeing lakes that fill or drain in half a year. In one case, 3 cubic kilometers of water drained last year from one of these lakes. That’s about the size of Lake Washington in Seattle.

My main objective in all of this is to figure out where that water went and how it has affected other subglacial lakes and glaciers downstream. Have those glaciers sped up from the water flowing under them? The warmth of the surface bed beneath glaciers allows them to slide faster. If you add more water, there’s potential for glaciers to slide faster.

I’m also part of a team that is helping to design the ICESat II satellite – a project we hope will build on the success of ICESat I. The satellite will boast several laser beams rather than one, so it’ll provide much better spatial coverage of the Earth’s surface to measure glacier mass and area.

President Obama honored PECASE awardees, including Ben Smith and Josh Willis, in January at the White House. Credit: The White House

WhatOnEarth: Were you aware that you’d been nominated for the PECASE award?

Smith: No. I was completely unaware of it until I was notified by the FBI about a background check! I can tell you I was relieved when I found out the background check regarded my visit to the White House. I understand now that my nomination was put forward by colleagues at NASA. Somehow, my nomination came out on top of the pile, and that’s pretty cool.

To read a few of Ben Smith’s ICESat-related scientific papers, click the topics below.

A image from a simulation that shows the spread of black carbon aerosols in Asia. Areas where the air was thick with the pollution particles are white, while lower concentrations are transparent purple. (Credit: Earth Observatory)

Yet pinning down precisely how much the black carbon exacerbates warming is no easy task, research conducted by Goddard Institute for Space Studies climatologist Dorothy Koch suggests. The study, published in Atmospheric Chemistry and Physics tracked how the predictions from 17 global black carbon models compared with actual measurements collected by airplane, satellite, and ground-based sensors. It shows, among other things, that models generally underestimate black carbon’s warming effect on climate.

Koch tested all the models in three ways. In the simplest of the three, she compared the models’ predictions to the amount of black carbon measured at the surface, finding that they matched real life reasonably well.

Her second test compared the models’ predictions to black carbon measurements made higher in the atmosphere using airplanes, and the results were much less clear cut. Though the models usually had too much black carbon over pollution sources, most had too little over remote regions such as the Arctic.

Koch’s final and most important test looked at how much solar radiation black carbon actually absorbs, an indicator of the amount of warming the particles actually produce. Again, the results were mixed. The models were largely accurate over North America and Europe, but were not for areas that have high levels of black carbon such as Central Africa, Southeast Asia, and the Amazon.

We concluded from this study that most models have enough black carbon at ground level in polluted regions, too much in the atmosphere above source regions, but not enough in the Arctic where black carbon may play an important role in contributing to Arctic warming and ice/snow melt. The models’ soot generally does not absorb enough sunlight and therefore these models would underestimate black carbon heating effects. This probably results from underestimating the absorbing properties of the particles rather than the amount (mass) of black carbon.

Wondering how climate modelers can continue to close the gap between model predictions and reality? Koch put forward some advice on how to fine-tune the next generation of aerosols models. Her top three:

1) Account for mixing between black carbon and other components of the atmosphere, 2) Incorporate better measurements of particle size and source amount in some regions. 3) Continue to mine ongoing satellite and field campaigns for data about black carbon.

You can read more GISS science briefs and NASA news stories about black carbon here, here, and here.